nanotechnology

Ever hear of a piezo-optomechanical circuit? We hadn’t either. Let’s break it down. Piezo implies some transducer that converts motion to and from energy. Opto implies light. Mechanical implies…well, mechanics. The device, from National Institute of Standards and Technology (NIST), converts signals among optical, acoustic and radio waves. They claim a system based on this design could move and store information in future computers.

At the heart of this circuit is an optomechanical cavity, in the form of a suspended nanoscale beam. Within the beam are a series of holes that act as mirrors for very specific photons. The photons bounce back and forth thousands of times before escaping the cavity. Simultaneously, the nanoscale beam confines phonons, that is, mechanical vibrations. The photons and phonons exchange energy. Vibrations of the beam influence the buildup of photons and the photons influence the mechanical vibrations. The strength of this mutual interaction, or coupling, is one of the largest reported for an optomechanical system.

In addition to the cavities, the device includes acoustic waveguides. By channeling phonons into the optomechanical device, the device can manipulate the motion of the nanoscale beam directly and, thus, change the properties of the light trapped in the device. An “interdigitated transducer” (IDT), which is a type of piezoelectric transducer like the ones used in surface wave devices, allows linking radio frequency electromagnetic waves, light, and acoustic waves.

The work appeared in Nature Photonics and was also the subject of a presentation at the March 2016 meeting of the American Physical Society. We’ve covered piezo transducers before, and while we’ve seen some unusual uses, we’ve never covered anything this exotic.

As circuits find their way into more and more real-world environments, the old standard circuitry isn’t always up to the task. It wasn’t that long ago that a computer needed special power, cooling, and a large room. Now those computers wouldn’t cut it for the top-of-the-line smartphone. However, most modern circuits don’t bend well and don’t like getting wet.

An international team of researchers is developing chemical-based circuitry that uses gold nanoparticles and electrically charged organic molecules to build circuit elements that behave like semiconductor diode junctions. It’s simple to make flexible circuits that don’t mind being wet using this chemical soup.

In an interview with IEEE Spectrum, the developers mentioned that other circuit elements similar to transistors and light sensors should be possible. The circuits aren’t perfect, however. The switching speed needs improvement. Also, while conventional circuits don’t like to get wet, these chemical circuits have difficulties if things get dry. Still, like all technology, things will probably improve over time.

This technology needs a good bit of engineering refinement before it is practical. If you need flexible photosensitive circuits in the near term, you might try here. Meanwhile, waterproof circuitry just needs the right kind of enclosure.

I recently finished the Silo series by Hugh Howey, a self-published collection of novellas that details life in a near-future, post-apocalyptic world where all that remains of humanity has been stuffed into subterranean silos. It has a great plot with some fun twists and plenty of details to keep the hacker and sci-fi fan entertained.

One such detail is nanorobots, used in later volumes of the series as both life-extending tools and viciously specific bio-weapons. Like all good reads, Silo is mainly character driven, so Howey doesn’t spend a lot of eInk on describing these microscopic machines – just enough detail to move the plot along. But it left me wondering about the potential for nanorobotics, and where we are today with the field that dates back to Richard Feynman’s suggestion that humans would some day “swallow the doctor” in a 1959 lecture and essay called “There’s Plenty of Room at the Bottom.”

Sometimes a hack needs something more than duct tape. Cyanoacrylate glue is great, if you don’t mind sticking your fingers together. But it doesn’t stick to everything, nor does it fill gaps. Epoxy is strong, but isn’t nearly as convenient. The point is, one type of glue doesn’t fit every situation, and that’s why you have to keep a lot of options. [Syuji Fujii] of Japan’s Osaka Institute of Technology (and his colleagues) have a new option: a glue that goes on dry and sticks when squished.

According to New Scientist, the researchers rolled spheres of a latex liquid in a layer of calcium-carbonate nanoparticles. The resulting spheres are a few millimeters across and pour easily. When put under pressure for a few seconds, the nanoparticles are pushed inside, and the sticky liquid contacts the surface. The source paper is also available if you want to read the gory details. Or you can cut right to the video below to see it in action.

If you don’t think glue is a good hacking material, you don’t know [Kevin Dady]. You can even glue wires if you really hate soldering, although we’d rather solder.

Traditionally, capacitors are like really bad rechargeable batteries. Supercapacitors changed that, making it practical to use a fast-charging capacitor in place of rechargeable batteries. However, supercapacitors work in a different way than conventional (dielectric) capacitors. They use either an electrostatic scheme to achieve very close separation of charge (as little as 0.3 nanometers) or electrochemical pseudocapacitance (or sometime a combination of those methods).

In a conventional capacitor the two electrodes are as close together as practical and as large as practical because the capacitance goes up with surface area and down with distance between the plates. Unfortunately, for high-performance energy storage, capacitors (of the conventional kind) have a problem: you can get high capacitance or high breakdown voltage, but not both. That’s intuitive since getting the plates closer makes for higher capacitance but also makes the dielectric more likely to break down as the electric field inside the capacitor becomes higher with both voltage and closer plate spacing (the electric field, E, is equal to the voltage divided by the plate spacing).

[Guowen Meng] and others from several Chinese and US universities recently published a paper in the journal Science Advances that offers a way around this problem. By using a 3D carbon nanotube electrode, they can improve a dielectric capacitor to perform nearly as well as a supercapacitor (they are claiming 2Wh/kg energy density in their device).

The capacitor forms in a nanoporous membrane of anodic aluminum oxide. The pores do not go all the way through, but stop short, forming a barrier layer at the bottom of each pore. Some of the pores go through the material in one direction, and the rest go through in the other direction. The researchers deposited nanotubes in the pores and these tubes form the plates of the capacitor (see picture, right). The result is a capacitor with a high-capacity (due to the large surface area) but with an enhanced breakdown voltage thanks to the uniform pore walls.

To improve performance, the pores in the aluminum oxide are formed so that one large pore pointing in one direction is surrounded by six smaller pores going in the other direction (see picture to left). In this configuration, the capacitance in a 1 micron thick membrane could be as high as 9.8 microfarads per square centimeter.

For comparison, most high-value conventional capacitors are electrolytic and use two different plates: a plate of metallic foil and a semi-liquid electrolyte. You can even make one of these at home, if you are so inclined (see video below).

It is amazing to think how a new technology like carbon nanotubes can make something as old and simple as a capacitor better. You have to wonder what other improvements will come as we understand these new materials even better.

I collect slide rules. You probably know a slide rule is a mechanical calculator of sorts. They usually look like a ruler (hence the name) and have a sliding part (hence the name) and by using logarithms you can multiply and divide easily by doing number line addition and subtraction (among other things).

It is easy to dismiss old technology like that out of hand as being antiquated, but mechanical computing may be making a comeback. It may seem ancient, but mechanical adding machines, cash registers, and even weapon control computers were all mechanical devices a few decades ago and there were some pretty sophisticated techniques developed to make them work. Perhaps the most sophisticated of all was Babbage’s difference engine, even though he didn’t have the technology to make one that actually functioned (the Computer History Museum did though; you should see it operating in person, but this is good too).

Using multiwall carbon nanotubes, researchers at Georgia Institute of Technology have created what they say are the first optical rectennas–antennas with rectifiers that produce DC current. The work could lead to new technology for advanced photodetectors, new ways to convert waste heat to electricity and, possibly, more efficient ways to capture solar energy.

A paper in Nature Nanotechnology describes how light striking the nanotube antennas create a charge that moves through attached rectifiers. Challenges included making the antennas small enough for optical wavelengths, and creating diodes small enough and fast enough to work at the extremely short wavelengths. The rectifiers switch on and off at petahertz speeds (something the Institute says is a record). Continue reading “Optical Rectenna Converts Light to DC”→